tshoot排错v2.0300-交换4课时

LAN

Switching

ReviewTroubleshooting

requires

detailed

process

knowledge.Which

processes

take

place

when

frames

are

send

and

switched

fromHost

A

to

Host

B

andback?Host

AHost

BSwitch

CSwitch

DSwitch

ETrunkTrunkVLAN

10VLAN

10CCNP

TShoot排错v2.0

(300-135)二层数据帧的格式IEEE802.3和以太网的封装格式类型0806ARP

请求/应答PAD类型0835RARP

请求/应答PAD802.3MAC

802.2

LLC802.2

SNAP目的地址源地址长度DSAPAASSAPAAcntl0

3code0

0类型数

据CRC6

6

2以太网封装(RFC

894):1

1

1

3

2

38~1492类型

IP

数据报08002

38~14922

28

10

2

28

1046~1500字节4目的地址源地址类型数

据CRC662446~1500类型0800IP

数据报246~类型ARP

请求/应答PAD10228类型0835RARP

请求/应答PAD10802.3

帧10101011SA:源MAC地址SFD:

帧开始标志,DA:

目的

MAC地址LEN:

LLC帧长度DATA:

数据字段PAD:填充字段CRC:校验字段字节7到字节or

34PRESFDDA

SA

LENLLC

控制信息DATAPAD

CRCLLC

帧PRE:

先导字节,

7个10101010以太网II型帧目的地址源地址类型数

据CRC以太网封装(RFC894):

46~1500字节662446~1500类型0800IP

数据包246~类型ARP

请求/应答PAD10DASACRCtagTPIDPriority标准以太网帧Type

DataTCICFI VLAN

ID带有IEEE802.1Q标记的以太网帧Ethernet

II,

Src:

Giga-Byt_bb:67:40

(00:1d:7d:bb:67:40),

Dst:

M&S_66:2f:80

(00:0c:58:66:2f:80)Destination:

M&S_66:2f:80

(00:0c:58:66:2f:80)Source:Giga-Byt_bb:67:40

(00:1d:7d:bb:67:40)Type:

802.1Q

Virtual

LAN

(0x8100)802.1Q

Virtual

LAN,

PRI:

0,

CFI:

0,

ID:

20000.

....

....

....

=Priority:

0...0

....

....

....

=CFI:

0....

0000

0001

0100

=

ID:20Type:

IP

(0x0800)Internet

Protocol,

Src:

20.20.20.20

(20.20.20.20),

Dst:10.10.10.10

(10.10.10.10)Internet

Control

Message

Protocol目的地址源地址类型数据CRCVLAN的帧格式66246~15004CCNP

TShoot排错v2.0

(300-135)触发的ARP解析过程Layer

2

Switching

ProcessUser

initiates

a

connection.Switch

CSwitch

DSwitch

ETrunkTrunkC:\

10.1.1.2Host

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10Layer

2

Switching

Process(Cont.)Host

A

sends

an

ARP

request

as

a

broadcast.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ARPDMACSMACTYPEDATAFCSBCASTMAC

A0X0806ARP

RequstCRCLayer

2

Switching

Process

(Cont.)The

switches

C

flood

the

ARP

broadcast

on

all

ports

in

VLAN10including

trunks

.The

switches

C

will

learning

the

MAC

address

of

Host A

in

the

process.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ARPARPARPDMACSMACTYPE802.1QTYPEDATAFCSBCASTMAC

A0X8100VLAN

100X0806ARP

RequstCRCLayer

2

Switching

Process

(Cont.)Host

B

responds

to

the

ARP

using

uncast

to

Host

A.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ARPDMACSMACTYPEDATAFCSMAC

AMAC

B0X0806ARP

ReplyCRCLayer

2

Switching

Process

(Cont.)The

switches

forwardthe

ARP

reply

on

the

port

on

which

they

learnedthe

MAC

addressof

Host

A，at

the

sametime

recording

theMACaddress

of

Host

B.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ARPDMACSMACTYPE802.1QTYPEDATAFCSMAC

AMAC

B0x8100VLAN

100X0806ARP

ReplyCRCARPARPCCNP

TShoot排错v2.0

(300-135)ICPM收发过程Layer

2

Switching

Process

(Cont.)Host

A

now

send

the

original

packet

as

a

unicast

to

Host

B，and

theswitch

forwardon

their

port

toward

Host

B.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ICMPICMPICMPDMACSMACTYPE802.1QTYPEDATAFCSMAC

BMAC

A0x8100VLAN

100x0800ICMP

Echo

RequstCRCICMPLayer

2

Switching

Process

(Cont.)Host

B

responds

using

unicast

Host

A，and

the

switches

forward

thisframe

on

their

port

towardHost

A.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10ICMPICMPICMPDMACSMACTYPE802.1QTYPEDATAFCSMAC

BMAC

A0x8100VLAN

100x0800ICMP

Echo

ReplyCRCICMPLayer

2

Switching

Process

(Cont.)This

completes

the

exchange.Switch

CSwitch

DSwitch

ETrunkTrunkHost

A10.1.1.1/24Host

B10.1.1.2/24C:\

10.1.1.2ing

10.1.1.2

with

32

bytes

ofdata:Reply

from

10.1.1.2

:

bytes=32

time=2ms

TTL=64VLAN

10VLAN

10CCNP

TShoot排错v2.0

(300-135)典型的局域网交换故障分析Discussion

：Typical

LAN

Switching

ProblemsWhat

can

cause

this

process

to

fail?How

can

you

determine

where

it

fails?What

commands

can

you

use

to

diagnose

these

problems?Switch

CSwitch

DSwitch

ETrunkTrunkC:\

10.1.1.2ing

10.1.1.2

with

32

bytes

ofdata:Reply

timed

out.Host

A10.1.1.1/24Host

B10.1.1.2/24VLAN

10VLAN

10Layer

2

Frame

Forwarding

InformationSwitches

use

the

following

information

in

their

Layer

2frame

forwarding

process：MAC

address

tableVLAN

databasePort-to-VLAN

mapTrunk

portsettingsVerifying

Layer

2

ForwardingHow

can

you

verify

correct

layer

2

forwarding?MAC

address

table：